Conventionally, as an apparatus for displaying a large-screen image, it is known a liquid crystal projector configured such that light from an illuminating device is irradiated on a liquid crystal display panel, and an image displayed on the liquid crystal display panel is projected on a screen. There is a liquid crystal projector that uses a multiple-light type illuminating device using a plurality of light sources as the illuminating device (see Japanese Patent Laying-open No.2002-296679). As shown in FIG. 9, a multiple-light type illuminating device 50 is so configured as to combine light fluxes emitted from a first light source 51 and a second light source 52 by a reflection mixing member 53. The reflection mixing member 53, also as shown in FIG. 7, has first reflecting surfaces 53a and second reflecting surfaces 53b one after another. The reflection mixing member 53 is also referred to as a prism array. By using a plurality of small light sources in such the multiple-light type illuminating device 50, it becomes possible to have better lifetime of light sources and higher efficiency of a convergence of light because an arc length of each light source is shortened, and it becomes also possible to continue projecting even if light-emitting stops (e.g., lamps are dead) due to an expiration of an operating life of the light sources.
Incidentally, a configuration in which an integrator lens is arranged on a light-exit side of the reflection mixing member 53 is adopted in many cases. The integrator lens is formed of a pair of fly's eye lenses and is designed such that each pair of convex lenses guides light from the light sources onto an entire surface of a liquid crystal display panel, so that partial luminance non-uniformity existing in the light emitted from the light sources is evened off and a difference between a light amount at a screen center and that at a screen perimeter is reduced.
However, in the configuration in which the integrator lens is arranged on the light-exit side of the reflection mixing member 53, as shown in FIG. 6, in a case that a ratio of a pitch Wp of a triangular prism formed of the first reflecting surface 53a and the second reflecting surface 53b in the reflection mixing member 53 to a lens pitch Wf of a light-incidence side fly's eye lens 55 of the integrator lens is 1 to 1, for example, light fluxes having the same pattern are incident on each lens portion 55a of the fly's eye lens 55, and the light fluxes having the same pattern are converged on a liquid crystal display panel 55. As a result, luminance non-uniformity is generated in the light incident on the liquid crystal display panel.
Furthermore, in the configuration in which the integrator lens is arranged on the light-exit side of the reflection mixing member 53, as shown in FIG. 8, as might be expected, light is guided from the reflection mixing member 53 both onto an upper area and a lower area of a light-incidence surface of the light-incidence side fly's eye lens 55 of the integrator lens in the same luminance non-uniformity pattern. Therefore, if the pattern of light flux guided to the liquid crystal display panel (LCD) by each pair of lenses on the upper area is the pattern in a frame described as “upper half” in FIG. 8, the pattern of light flux guided to the liquid crystal display panel (LCD) by each pair of lenses on the lower area is the same pattern (see “lower half” in FIG. 8). As a result of this, the above-described pattern is emphasized on the liquid crystal display panel (LCD), so that the luminance non-uniformity is generated in a projected image.
In a projector using three liquid crystal display panels, in particular, a configuration in which an optical path length of one color out of three primary colors is different is adopted for reducing in size of a color separating and mixing system and a relay optical system is used so that the optical path length of one color is optically coincident with that of the other two colors. Accordingly, light is incident on the liquid crystal display panel in a state that the only one color mentioned above is reversed to right to left and up to down with respect to the other two colors. As a result, a difference in luminance distribution between the one color and the other two colors is generated. This difference in luminance distribution of respective colors generates luminance non-uniformity and color non-uniformity in a projected image on a screen. For eyes of human being, it is easier to perceive color non-uniformity than luminance non-uniformity, so that this color non-uniformity greatly reduces a quality of a displayed image.